Multispiral for a pre-heating pencil spark plug

ABSTRACT

A sheathed-element glow plug, in particular for internal combustion engines, includes a housing, a glow plug situated on the housing and having a heating and regulating filament situated in the glow tube, current being applicable to this heating and regulating filament via a terminal stud situated in the housing. The control filament r the heating filament or the heating and control filament are optionally multiple-coil filaments.

FIELD OF THE INVENTION

The present invention relates to a sheathed-element glow plug, inparticular for internal combustion engines, composed essentially of ahousing, a heating element situated on the housing and having a heatingand regulating filament situated in the glow tube, current beingapplicable to this heating and regulating filament via a terminal studsituated in the housing.

BACKGROUND INFORMATION

Internal combustion engines, in particular diesel engines, need anadditional heat source for preheating the gas mixture, the intake air,or the combustion chamber for starting and warm-up, in particular at lowtemperatures.

In passenger cars and sometimes in trucks, sheathed-element glow plugsmay be provided and used for this purpose. At least part of the heatingelement of such a sheathed-element glow plug protrudes into thecombustion chamber of the engine and preheats the combustion chamberbefore the actual engine start and in cold run. In addition, the fuelmay ignite on the hot surface of the sheathed-element glow plug.

Sheathed-element glow plugs may be made of a plug housing having a glowtube or a tubular heating element situated thereon. A glow filament,embedded in a compacted magnesium oxide powder, is situated in thetubular heating element made of a material resistant to corrosion by hotgases. The glow filament is usually made of two resistors connected inseries: a control filament and a heating filament. The heating filamenthas an electrical resistance which is almost independent of thetemperature, and the control filament is made of a material having apositive temperature coefficient (PTC). The heating filament is weldedinto the cap of the glow tube on the ground side for contacting. Thecontrol filament is contacted to the terminal stud which is connected tothe vehicle electrical system.

When a voltage is applied to the glow plug, most of the electric poweris converted into heat in the heating filament, and the temperature atthe tip of the plug increases steeply. The temperature of the controlfilament, and thus also its resistance, increase with a time delay.Current consumption and thus the total power consumption of thesheathed-element glow plug are reduced and the temperature approaches astate of equilibrium. Currently sheathed-element glow plugs designed for12 V to 24 V vehicle electrical systems are commercially available.

SUMMARY OF THE INVENTION

An object of the exemplary embodiment and/or exemplary method of thepresent invention is to concentrate the heating power on the glow tubetip of the sheathed-element glow plug, making the latter also availablefor 42 V vehicle electrical systems.

The exemplary embodiment and/or exemplary method of the presentinvention involves packing more heating wire and thus more electricalresistance into the same space using multiple filaments. Previously,typical sheathed-element glow plugs have only had single coil filaments.In the sheathed-element glow plugs according to exemplary embodiment ofthe present invention, the heating filaments, the control filaments, orboth, may have multiple coil filaments as required.

It is believed that an advantage of packing more heating wire into atight space is that the heating power may be increased, in particular atthe glow tube tip.

More wire in a tight space also means with respect to the heating andcontrol filaments that a higher resistance is achieved and thereforehigher voltages are made possible, in particular for those designed forthe planned 42-V vehicle electrical systems.

The filaments may be advantageously designed in different ways byproducing the individual filaments wound in the same direction or inopposite directions.

In particular when winding the filaments in opposite directions, theadvantage is that the overall filament has a reduced outer diameter, andtherefore a very compact design is obtained, which also has theadvantage that existing glow tubes do not need to be modified.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a section of a sheathed-element glow plug according to thepresent invention and having a multiple-coil heating filament at theglow tube tip.

FIG. 2 shows an exemplary embodiment of an exemplary configuration ofthe multiple-coil heating filament illustrated in FIG. 1.

FIG. 3 shows a schematic diagram of the current flow in the multiplewinding of the filaments illustrated in FIG. 2, the filaments beingwound in opposite directions.

FIG. 4 shows a schematic top view of filaments wound in the samedirection.

FIG. 5 shows a schematic top view with the middle filament wound in theopposite direction.

FIG. 6 shows a two-layer example with both filaments wound in the samedirection.

FIG. 7 shows a two-layer example with the two filaments wound inopposite directions.

DETAILED DESCRIPTION

FIG. 1 shows the structure of a sheathed-element glow plug 1. Thissheathed-element glow plug 1 has a housing 2 and a glow tube 3 situatedon the housing. A heating and control filament 4 is situated in glowtube 3, heating filament 5 being in the area of glow plug tip 6 andcontrol filament 7 in the part above it. Heating and control filament 4is supplied with power via a terminal stud 8.

As depicted in FIG. 1, at least one part, either heating filament 5 orcontrol filament 7, is a multiple-coil filament.

In the exemplary embodiment of FIG. 1, heating filament 5 is amultiple-coil filament.

There are different embodiments for implementing the multiple winding ofcontrol filament 7 or heating filament 5.

FIG. 2 shows an enlarged depiction of heating filament 5 illustrated inFIG. 1. The manufacturing of heating filament 5 begins with a diameterd1, the other winding having a larger diameter such as d2 being joineddirectly to the end of the first filament. The third filament having adiameter such as d3 is joined to the end of filament 2, so that thecurrent flows as shown in FIGS. 3 and 4.

The filament layers may be wound in the same direction. In this case,the filaments cannot be wound as tightly, because the individualfilaments cross one another. The following inequality applies:wd3>wd2+dd>wd1+dd. Alternatively, the direction of winding may beinverted in each layer. In this case, the additional filament may be inthe groove of the adjacent filament. In this way, a smaller outerdiameter may be achieved than in the case of the type of winding of FIG.2.

A high-performance sheathed-element glow plug is obtained by the simplemultiple-coil design.

1-4. (canceled)
 5. A sheathed-element glow plug for an internal combustion engine, comprising: a housing; a glow tube situated on the housing and having a heating filament and a control filament situated in the glow tube, current being appliable to the heating and regulating filament via a terminal stud situated in the housing, wherein the at least one of the control filament and the heating filament is a multiple-coil filament.
 6. The sheathed-element glow plug of claim 5, wherein a winding diameter of a first filament of the filaments has a smallest diameter and other of the filaments having individual filament diameters have larger winding diameters.
 7. The sheathed-element glow plug of claim 6, wherein the filaments having individual filament diameters are wound in a same direction.
 8. The sheathed-element glow plug of claim 6, wherein the filaments having the individual filament diameters are wound in opposite directions. 